In recent years, ventricular assist device has been used in cases where it is impossible to well maintain systemic circulation due to deterioration in the pumping function of the subject's heart after cardiovascular surgery, on acute myocardial infarction, etc. In such cases, left heart failure is often dominant, and a ventricular assist device is normally placed in parallel to the left heart of the patient, which serves to supplement the pumping function of the failed heart for a given time and facilitates the functional recovery of the failed heart while maintaining systemic circulation. The bypass flow from the ventricular assist device is decreased according to the degree of functional recovery of the failed heart so that systemic circulation remains constant. Since the ventricular assist device involves the possibility of thrombos formation due to too low a blood flow rate in cases where the bypass flow decreases below a certain level, an intra-aortic balloon catheter (hereinafter referred to as balloon) is normally sued after weaning. When the bypass flow from the ventricular assist device has decreased below a given level, the ventricular assist device is removed and assist circulation is maintained using the balloon alone. Also known is the method in which the ventricular assist device drive console and the balloon drive console are electrocardiographically synchronized to be 1 cycle each per 2 beats of the failed heart (patient's heart) so that the ventricular assist device and the balloon are alternatively driven at a rate of 1 cycle per beat of the failed heart.
When using a ventricular assist device and a balloon in combination, simultaneous occurrence of ventricular assist device systole and balloon inflation causes abnormal increase in aortic pressure, which suppresses output flow from the ventricular assist device and poses a circulation management problem. Already proposed methods include the method in which he diastole is divided into two periods, allotted to the ventricular assist device and the balloon, respectively, and driving timing is adjusted so that ventricular assist device systole and balloon inflation do not occur simultaneously. However, this method is subject to significant limitation on driving conditions and is unsuitable for weaning, since dividing the diastole requires quick driving of the ventricular assist device and balloon. In the above-mentioned method in which the ventricular assist device drive and the balloon drive are electrocardiographically synchronized so that the ventricular assist device and the balloon are alternatively driven at a rate of 1 cycle per beat of the patient's heart. It is necessary to constantly monitor and adjust the operation to ensure alternative driving, since the ventricular assist device and the balloon are sometimes driven simultaneously because their controllers act separately due to electrocardiographic disturbance. In addition, for successful weaning from the ventricular assist device, it is desirable that the balloon driving frequency per beat of the ventricular assist device be increased gradually to reach a given ratio of balloon driving, and then the synchronous ratio of the ventricular assist device to the natural heart be decreased to be removed; however, this is difficult to achieve with conventional assist circulation apparatuses.